Device and method for vaporizing temperature sensitive materials

ABSTRACT

A method for vaporizing organic materials onto a substrate surface to form a film including providing a quantity of organic material into a vaporization apparatus and actively maintaining the organic material in a first heating region in the vaporization apparatus to be below the vaporization temperature. The method also includes heating a second heating region of the vaporization apparatus above the vaporization temperature of the organic material and metering, at a controlled rate, organic material from the first heating region into the second heating region so that a thin cross section of the organic material is heated at a desired rate-dependent vaporization temperature, whereby organic material vaporizes and forms a film on the substrate surface.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned U.S. patent application Ser. No.10/352,558 filed Jan. 28, 2003 by Jeremy M. Grace et al., entitled“Method of Designing a Thermal Physical Vapor Deposition System”, thedisclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the field of physical vapor depositionwhere a source material is heated to a temperature so as to causevaporization and produce a vapor plume to form a thin film on a surfaceof a substrate.

BACKGROUND OF THE INVENTION

An OLED device includes a substrate, an anode, a hole-transporting layermade of an organic compound, an organic luminescent layer with suitabledopants, an organic electron-transporting layer, and a cathode. OLEDdevices are attractive because of their low driving voltage, highluminance, wide-angle viewing and capability for full-color flatemission displays. Tang et al. described this multilayer OLED device intheir U.S. Pat. Nos. 4,769,292 and 4,885,211.

Physical vapor deposition in a vacuum environment is the principal wayof depositing thin organic material films as used in small molecule OLEDdevices. Such methods are well known, for example, Barr in U.S. Pat. No.2,447,789 and Tanabe et al. in EP 0 982 411. The organic materials usedin the manufacture of OLED devices are often subject to degradation whenmaintained at or near the desired rate-dependent vaporizationtemperature for extended periods of time. Exposure of sensitive organicmaterials to higher temperatures can cause changes in the structure ofthe molecules and associated changes in material properties.

To overcome the thermal sensitivity of these materials, only smallquantities of organic materials have been loaded in sources, and theyare heated as little as possible. In this manner, the material isconsumed before it has reached the temperature exposure threshold tocause significant degradation. The limitations with this practice arethat the available vaporization rate is very low due to the limitationon heater temperature, and the operation time of the source is veryshort due to the small quantity of material present in the source. Thelow deposition rate and frequent source recharging place substantiallimitations on the throughput of OLED manufacturing facilities.

A secondary consequence of heating the entire organic material charge toroughly the same temperature is that it is impractical to mix additionalorganic materials, such as dopants, with a host material unless thevaporization behavior and vapor pressure of the dopant is very close tothat of the host material. This is generally not the case and, as aresult, prior art devices frequently require the use of separate sourcesto co-deposit host and dopant materials.

The organic materials used in OLED devices have a highly non-linearvaporization rate dependence on source temperature. A small change insource temperature leads to a very large change in vaporization rate.Despite this, prior art devices employ source temperature as the onlyway to control vaporization rate. To achieve good temperature control,prior art deposition sources typically utilize heating structures whosesolid volume is much larger than the organic charge volume, composed ofhigh thermal-conductivity materials that are well insulated. The highthermal conductivity insures good temperature uniformity through thestructure, and the large thermal mass helps to maintain the temperaturewithin a critically small range by reducing temperature fluctuations.These measures have the desired effect on steady-state vaporization ratestability but have a detrimental effect at start-up. It is common thatthese devices must operate for many hours at start-up beforesteady-state thermal equilibrium and hence a steady vaporization rate isachieved.

A further limitation of prior art sources is that the geometry of thevapor manifold changes as the organic material charge is consumed. Thischange requires that the heater temperature change to maintain aconstant vaporization rate, and it is observed that the plume shape ofthe vapor exiting the orifices changes as a function of the organicmaterial thickness and distribution in the source.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a deviceand method for vaporizing organic materials while limiting theirexposure to temperatures that can cause material degradation. It is afurther object of this invention to permit a single source to deposittwo or more organic material components. It is a further object of thisinvention to achieve a steady vaporization rate quickly. It is a furtherobject to maintain a steady vaporization rate with a large charge oforganic material and with a steady heater temperature.

This object is achieved by a method for vaporizing organic materialsonto a substrate surface to form a film, comprising:

a) providing a quantity of organic material into a vaporizationapparatus;

b) actively maintaining the organic material in a first heating regionin the vaporization apparatus to be below the vaporization temperature;

c) heating a second heating region of the vaporization apparatus abovethe vaporization temperature of the organic material; and

d) metering, at a controlled rate, organic material from the firstregion into the second heating region so that a thin cross section ofthe organic material is heated at a desired rate-dependent vaporizationtemperature, whereby organic material sublimes and forms a film on thesubstrate surface.

ADVANTAGES

It is an advantage of the present invention that the device overcomesthe heating and volume limitations of prior art devices in that only asmall portion of organic material is heated to the desiredrate-dependent vaporization temperature at a controlled rate. It istherefore a feature of the present invention to maintain a steadyvaporization rate with a large charge of organic material and with asteady heater temperature. The device thus permits extended operation ofthe source with substantially reduced risk of degrading even verytemperature sensitive organic materials. This feature additionallypermits materials having different vaporization rates and degradationtemperature thresholds to be co-sublimated in the same source.

It is a further advantage of the present invention that it permits finerrate control and additionally offers an independent measure of thevaporization rate.

It is a further advantage of the present invention that it can be cooledand reheated in a matter of seconds to stop and reinitiate vaporizationand achieve a steady vaporization rate quickly. This feature minimizescontamination of the deposition chamber walls and conserves the organicmaterials when a substrate is not being coated.

It is a further advantage that the present device achieves substantiallyhigher vaporization rates than in prior art devices without materialdegradation. Further still, no heater temperature change is required asthe source material is consumed.

It is a further advantage of the present invention that it can provide avapor source in any orientation, which is not possible with prior artdevices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a device accordingto the present invention including a piston and a drive mechanism as away for metering organic material into a heating region;

FIG. 2 shows a graphical representation of vapor pressure vs.temperature for two organic materials;

FIG. 3 is a cross-sectional view of another embodiment of a deviceaccording to the present invention including a liquid metal as a way formetering organic material into a heating region and to form a seal toprevent vapors from escaping;

FIG. 4 is a cross-sectional view of a third embodiment of a deviceaccording to the present invention including a rotating drum having asurface pattern of recesses as a way for metering organic material intoa heating region;

FIG. 5 is a cross-sectional view of a device according to the presentinvention including a deposition chamber enclosing a substrate; and

FIG. 6 is a cross-sectional view of an OLED device structure that can beprepared with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to FIG. 1, there is shown a cross-sectional view of oneembodiment of a device of this disclosure. Vaporization apparatus 5 is adevice for vaporizing organic materials onto a substrate surface to forma film, and includes a first heating region 25 and a second heatingregion 35 spaced from first heating region 25. First heating region 25includes a first heating means represented by base block 20, which canbe a heating base block or a cooling base block, or both, and which caninclude control passage 30. Chamber 15 can receive a quantity of organicmaterial 10. Second heating region 35 includes the region bounded bymanifold 60 and permeable member 40, which can be part of manifold 60.Manifold 60 also includes one or more apertures 90. A way of meteringorganic material includes chamber 15 for receiving the organic material10, piston 50 for raising organic material 10 in chamber 15, as well aspermeable member 40. Vaporization apparatus 5 also includes one or moreshields 70.

Organic material 10 is preferably either a compacted or pre-condensedsolid. However, organic material in powder form is also acceptable.Organic material 10 can comprise a single component, or can comprise twoor more organic components, each one having a different vaporizationtemperature. Organic material 10 is in close thermal contact with thefirst heating means that is base block 20. Control passages 30 throughthis block permit the flow of a temperature control fluid, that is, afluid adapted to either absorb heat from or deliver heat to the firstheating region 25. The fluid can be a gas or a liquid or a mixed phase.Vaporization apparatus 5 includes a way for pumping fluid throughcontrol passages 30. Such pumping means, not shown, are well known tothose skilled in the art. Through such means, organic material 10 isheated in first heating region 25 until it is a temperature below itsvaporization temperature. The vaporization temperature can be determinedby various ways. For example, FIG. 2 shows a graphical representation ofvapor pressure versus temperature for two organic materials commonlyused in OLED devices. The vaporization rate is proportional to the vaporpressure, so for a desired vaporization rate, the data in FIG. 2 can beused to define the required heating temperature corresponding to thedesired vaporization rate. First heating region 25 is maintained at aconstant heater temperature as organic material 10 is consumed.

Organic material 10 is metered at a controlled rate from first heatingregion 25 to second heating region 35. Second heating region 35 isheated to a temperature above the vaporization temperature of organicmaterial 10, or each of the organic components thereof. Because a givenorganic component vaporizes at different rates over a continuum oftemperatures, there is a logarithmic dependence of vaporization rate ontemperature. In choosing a desired deposition rate, one also determinesa necessary vaporization temperature of organic material 10, which willbe referred to as the desired rate-dependent vaporization temperature.The temperature of first heating region 25 is below the vaporizationtemperature, while the temperature of second heating region 35 is at orabove the desired rate-dependent vaporization temperature. In thisembodiment, second heating region 35 comprises the region bounded bymanifold 60 and permeable member 40. Organic material 10 is pushedagainst permeable member 40 by piston 50, which can be controlledthrough a force-controlled drive mechanism. Piston 50, chamber 15, andthe force-controlled drive mechanism comprise a way for metering. Thismetering means permits organic material 10 to be metered throughpermeable member 40 into second heating region 35 at a controlled ratethat varies linearly with the vaporization rate. Along with thetemperature of second heating region 35, this permits finer rate controlof the vaporization rate of organic material 10 and additionally offersan independent measure of the vaporization rate. A thin cross-section oforganic material 10 is heated to the desired rate-dependent temperature,which is the temperature of second heating region 35, by virtue ofcontact and thermal conduction, whereby the thin cross-section oforganic material 10 vaporizes. In the case where organic material 10comprises two or more organic components, the temperature of secondheating region 35 is chosen to be above the vaporization temperature ofeach of the components so that each of the organic material 10components simultaneously vaporizes. A steep thermal gradient on theorder of 200° C./mm is produced through the thickness of organicmaterial 10. This gradient protects all but the immediately vaporizingmaterial from the high temperatures. The vaporized organic vaporsrapidly pass through the permeable member 40 and can enter into a volumeof heated gas manifold 60 or pass directly on to the target substrate.Their residence time at the desired vaporization temperature is veryshort and, as a result, thermal degradation is greatly reduced. Theresidence time of organic material 10 at elevated temperature, that is,at the rate-dependent vaporization temperature, is orders of magnitudeless than prior art devices and methods (seconds vs. hours or days inthe prior art), which permits heating organic material 10 to highertemperatures than in the prior art. Thus, the current device and methodcan achieve substantially higher vaporization rates, without causingappreciable degradation of organic material 10. The constantvaporization rate, and constant volume of vaporizing organic material 10maintained in second heating region 35 establish and maintain a constantplume shape. The plume is herein defined as the vapor cloud exitingvaporization device 5.

Since second heating region 35 is maintained at a higher temperaturethan first heating region 25, it is possible that heat from secondheating region 35 can raise the temperature of the bulk of organicmaterial 10 above that of first heating region 25. Therefore, it isnecessary that the first heating means can also cool organic material 10after it rises above a predetermined temperature. This can beaccomplished by varying the temperature of the fluid in control passage30.

Where a manifold 60 is used, a pressure develops as vaporizationcontinues and streams of vapor exit the manifold 60 through the seriesof apertures 90. The conductance along the length of the manifold isdesigned to be roughly two orders of magnitude larger than the sum ofthe aperture conductances as described in commonly assigned U.S. patentapplication Ser. No. 10/352,558 filed Jan. 28, 2003 by Jeremy M. Graceet al., entitled “Method of Designing a Thermal Physical VaporDeposition System”, the disclosure of which is herein incorporated byreference. This conductance ratio promotes good pressure uniformitywithin manifold 60 and thereby minimizes flow non-uniformities throughapertures 90 distributed along the length of the source despitepotential local non-uniformities in vaporization rate.

One or more heat shields 70 are located adjacent the heated manifold 60for the purpose of reducing the heat radiated to the facing targetsubstrate. These heat shields are thermally connected to base block 20for the purpose of drawing heat away from the shields. The upper portionof shields 70 is designed to lie below the plane of the apertures forthe purpose of minimizing vapor condensation on their relatively coolsurfaces.

Because only a small portion of organic material 10, the portionresident in second heating region 35, is heated to the rate-dependentvaporization temperature, while the bulk of the material is kept wellbelow the vaporization temperature, it is possible to interrupt thevaporization by a way of interrupting heating in second heating region35, e.g. stopping the movement of piston 50. This can be done when asubstrate surface is not being coated so as to conserve organic material10 and minimize contamination of any associated apparatus, such as thewalls of a deposition chamber, which will be described below.

Because permeable member 40 can be a fine mesh screen that preventspowder or compacted material from passing freely through it,vaporization apparatus 5 can be used in any orientation. For example,vaporization apparatus 5 can be oriented 180° from what is shown in FIG.1 so as to coat a substrate placed below it. This is an advantage notfound in the heating boats of the prior art.

Although one preferred embodiment has been the use of vaporizationapparatus 5 with a powder or compressed material that sublimes whenheated, in some embodiments organic material 10 can be a material thatliquefies before vaporization, and can be a liquid at the temperature offirst heating region 25. In such a case, permeable member 40 can absorband retain liquefied organic material 10 in a controllable manner viacapillary action, thus permitting control of vaporization rate.

In practice, vaporization apparatus 5 can be used as follows. A quantityof organic material 10, which can comprise one or more components, isprovided into chamber 15 of vaporization apparatus 5. In first heatingregion 25, organic material 10 is actively maintained below thevaporization temperature of each of its organic components. Secondheating region 35 is heated to a temperature above the vaporizationtemperature of organic material 10 or each of the components thereof.Organic material 10 is metered at a controlled rate from first heatingregion 25 to second heating region 35. A thin cross-section of organicmaterial 10 is heated at a desired rate-dependent vaporizationtemperature, whereby organic material 10 vaporizes and forms a film on asubstrate surface. When organic material 10 comprises multiplecomponents, each component simultaneously vaporizes.

FIG. 3 shows a cross-sectional view of a second embodiment of a deviceof this disclosure. Vaporization apparatus 45 includes first heatingregion 25, second heating region 35, base block 20, control passages 30,chamber 15, manifold 60, apertures 90, shields 70, and permeable member40 as described above. Vaporization apparatus 45 does not include apiston, but instead includes liquid 65.

Organic material 10 can be as described above and is in close thermalcontact with base block 20. Organic material 10 is metered at acontrolled rate from first heating region 25 to second heating region35, which is heated to a temperature above the vaporization temperatureof organic material 10, or each of the components thereof. Organicmaterial 10 is pushed against permeable member 40 through contact with alow vapor pressure liquid 65. Liquid 65 must be a liquid at theoperating temperature of vaporization apparatus 45. For example, manyorganic materials commonly used in OLED devices have a vaporizationtemperature over 150° C. Therefore, it is sufficient that liquid 65 canbe liquid at 150° C. for such organic materials. Liquid 65 can providevery good thermal contact and a vapor-tight seal between organicmaterial 10 and base block 20. Low-melting liquid metals are suitablefor this purpose, including gallium, alloys of gallium and indium, aswell as controlled expansion alloys of bismuth and indium. Thesematerials have high thermal conductivity and serve to provide very goodthermal contact and a vapor-tight seal between the organic material andthe cooling block. Also suitable are low-vapor-pressure oils. Othermaterials are acceptable as liquid 65 to the extent that they do notreact with the organic material 10, have a higher density than organicmaterial 10, and have a vapor pressure much lower than the vaporpressure of organic material 10 over the temperature range employed invaporization apparatus 5. Organic material 10 floats on the surfaces ofsuch high surface tension, dense liquids and can be pushed againstpermeable member 40 with a very controllable force. This controlledforce, along with the temperature of permeable member 40, permitsprecise control of the vaporization rate of the organic material. A thincross-section of organic material 10 is heated to a desiredrate-dependent temperature, that is, the temperature of permeable member40, by virtue of contact and thermal conduction, whereby the thincross-section of organic material 10 vaporizes. A steep thermal gradienton the order of 200° C./mm is produced through the thickness of organicmaterial 10. This gradient protects all but the immediately vaporizingmaterial from the high temperatures. The vaporized organic vaporsrapidly pass through the permeable member 40 and can enter into a volumeof heated gas manifold 60 or pass directly on to the target substrate.Their residence time at the desired vaporization temperature is veryshort and, as a result, thermal degradation is greatly reduced.

Where a manifold 60 is used, a pressure develops as vaporizationcontinues and streams of vapor exit the manifold 60 through the seriesof apertures 90. The conductance along the length of the manifold isdesigned to be roughly two orders of magnitude larger than the sum ofthe aperture conductances as described by Grace et al. This conductanceratio promotes good pressure uniformity within manifold 60 and therebyminimizes flow non-uniformities through apertures 90 distributed alongthe length of the source, despite potential local non-uniformities invaporization rate.

Like vaporization apparatus 5, vaporization apparatus 45 can be adaptedto the use of a liquid organic material 10.

FIG. 4 shows a cross-sectional view of a third embodiment of a device ofthis disclosure. Vaporization apparatus 55 includes first heating region25, base block 20, control passages 30, chamber 15, manifold 60, andapertures 90 as described above.

Organic material 10 can be as described above and is in close thermalcontact with base block 20. Organic material 10 is pushed by either apiston or a liquid as described above against the periphery of rotatingdrum 105 and is carried as a fine powder film from first heating region25 to second heating region 35. The powder can be attracted to the drumby electrostatic forces and rotating drum 105 can have surface featuressuch as a knurled pattern or a pattern of small recesses having adefinite volume in which a controlled volume of organic material 10 iscontained so as to transport a fixed volume of powder. A wiper canoptionally be used to remove excess powder from the surface of rotatingdrum 105. Rotating drum 105 is preferably constructed such that itssurface has very little thermal mass, that is, the surface of rotatingdrum 105 is rapidly heated as it rotates to second heating region 35 andrapidly cools as it rotates back to first heating region 25.

Second heating region 35 includes a second heating means. The secondheating means can be incorporated in the surface of rotating drum 105through induction or RF coupling, it can include a radiant heatingelement in close proximity to the surface of rotating drum 105, or itcan include resistance heating means. The vaporization rate in thisembodiment is controlled by the rate of rotation of rotating drum 105,and the quantity of organic material 10 carried on its surface. Theheating mechanism simply insures that substantially all of organicmaterial 10 on the surface of rotating drum 105 is transformed to thevapor state. The vaporized organic vapors rapidly pass through secondheating region 35, and can enter into a volume of heated gas manifold 60or pass directly on to the target substrate. Their residence time attemperature is very short and, as a result, thermal degradation isgreatly reduced.

Where a manifold 60 is used, a pressure develops as vaporizationcontinues and streams of vapor exit the manifold 60 through the seriesof apertures 90. The conductance along the length of the manifold isdesigned to be roughly two orders of magnitude larger than the sum ofthe aperture conductances as described in commonly assigned U.S. patentapplication Ser. No. 10/352,558 filed Jan. 28, 2003 by Jeremy M. Graceet al., entitled “Method of Designing a Thermal Physical VaporDeposition System”, the disclosure of which is herein incorporated byreference. This conductance ratio promotes good pressure uniformitywithin manifold 60 and thereby minimizes flow non-uniformities throughapertures 90 distributed along the length of the source, despitepotential local non-uniformities in vaporization rate.

Like vaporization apparatus 5, vaporization apparatus 45 can be adaptedto the use of a liquid organic material 10.

Turning now to FIG. 5, there is shown an embodiment of a device of thisdisclosure including a deposition chamber enclosing a substrate.Deposition chamber 80 is an enclosed apparatus that permits an OLEDsubstrate 85 to be coated with organic material 10 transferred fromvaporization apparatus 5. Deposition chamber 80 is held under controlledconditions, e.g. a pressure of 1 Torr or less provided by vacuum source100. Deposition chamber 80 includes load lock 75 which can be used toload uncoated OLED substrates 85, and unload coated OLED substrates.OLED substrate 85 can be moved by translational apparatus 95 to provideeven coating of vaporized organic material 10 over the entire surface ofOLED substrate 85. Although vaporization apparatus is shown as partiallyenclosed by deposition chamber 80, it will be understood that otherarrangements are possible, including arrangements wherein vaporizationapparatus 5 is entirely enclosed by deposition chamber 80.

In practice, an OLED substrate 85 is placed in deposition chamber 80 viaload lock 75 and held by translational apparatus 95 or associatedapparatus. Vaporization apparatus 5 is operated as described above, andtranslational apparatus 95 moves OLED substrate 85 perpendicular to thedirection of emission of organic material 10 vapors from vaporizationapparatus 5, thus forming a film of organic material 10 on the surfaceof OLED substrate 85.

Turning now to FIG. 6, there is shown a cross-sectional view of a pixelof a light-emitting OLED device 110 that can be prepared in partaccording to the present invention. The OLED device 110 includes at aminimum a substrate 120, a cathode 190, an anode 130 spaced from cathode190, and a light-emitting layer 150. The OLED device can also include ahole-injecting layer 135, a hole-transporting layer 140, anelectron-transporting layer 155, and an electron-injecting layer 160.Hole-injecting layer 135, hole-transporting layer 140, light-emittinglayer 150, electron-transporting layer 155, and electron-injecting layer160 comprise a series of organic layers 170 disposed between anode 130and cathode 190. Organic layers 170 are the layers most desirablydeposited by the device and method of this invention. These componentswill be described in more detail.

Substrate 120 can be an organic solid, an inorganic solid, or includeorganic and inorganic solids. Substrate 120 can be rigid or flexible andcan be processed as separate individual pieces, such as sheets orwafers, or as a continuous roll. Typical substrate materials includeglass, plastic, metal, ceramic, semiconductor, metal oxide,semiconductor oxide, semiconductor nitride, or combinations thereof.Substrate 120 can be a homogeneous mixture of materials, a composite ofmaterials, or multiple layers of materials. Substrate 120 can be an OLEDsubstrate, that is a substrate commonly used for preparing OLED devices,e.g. active-matrix low-temperature polysilicon or amorphous-silicon TFTsubstrate. The substrate 120 can either be light transmissive or opaque,depending on the intended direction of light emission. The lighttransmissive property is desirable for viewing the EL emission throughthe substrate. Transparent glass or plastic are commonly employed insuch cases. For applications where the EL emission is viewed through thetop electrode, the transmissive characteristic of the bottom support isimmaterial, and therefore can be light transmissive, light absorbing orlight reflective. Substrates for use in this case include, but are notlimited to, glass, plastic, semiconductor materials, ceramics, andcircuit board materials, or any others commonly used in the formation ofOLED devices, which can be either passive-matrix devices oractive-matrix devices.

An electrode is formed over substrate 120 and is most commonlyconfigured as an anode 130. When EL emission is viewed through thesubstrate 120, anode 130 should be transparent or substantiallytransparent to the emission of interest. Common transparent anodematerials useful in this invention are indium-tin oxide and tin oxide,but other metal oxides can work including, but not limited to,aluminum-or indium-doped zinc oxide, magnesium-indium oxide, andnickel-tungsten oxide. In addition to these oxides, metal nitrides suchas gallium nitride, metal selenides such as zinc selenide, and metalsulfides such as zinc sulfide, can be used as an anode material. Forapplications where EL emission is viewed through the top electrode, thetransmissive characteristics of the anode material are immaterial andany conductive material can be used, transparent, opaque or reflective.Example conductors for this application include, but are not limited to,gold, iridium, molybdenum, palladium, and platinum. The preferred anodematerials, transmissive or otherwise, have a work function of 4.1 eV orgreater. Desired anode materials can be deposited by any suitable waysuch as evaporation, sputtering, chemical vapor deposition, orelectrochemical means. Anode materials can be patterned using well knownphotolithographic processes.

While not always necessary, it is often useful that a hole-injectinglayer 135 be formed over anode 130 in an organic light-emitting display.The hole-injecting material can serve to improve the film formationproperty of subsequent organic layers and to facilitate injection ofholes into the hole-transporting layer. Suitable materials for use inhole-injecting layer 135 include, but are not limited to, porphyriniccompounds as described in U.S. Pat. No. 4,720,432, plasma-depositedfluorocarbon polymers as described in U.S. Pat. No. 6,208,075, andinorganic oxides including vanadium oxide (VOx), molybdenum oxide(MoOx), nickel oxide (NiOx), etc. Alternative hole-injecting materialsreportedly useful in organic EL devices are described in EP 0 891 121 A1and EP 1 029 909 A1.

While not always necessary, it is often useful that a hole-transportinglayer 140 be formed and disposed over anode 130. Desiredhole-transporting materials can be deposited by any suitable way such asevaporation, sputtering, chemical vapor deposition, electrochemicalmeans, thermal transfer, or laser thermal transfer from a donormaterial, and can be deposited by the device and method describedherein. Hole-transporting materials useful in hole-transporting layer140 are well known to include compounds such as an aromatic tertiaryamine, where the latter is understood to be a compound containing atleast one trivalent nitrogen atom that is bonded only to carbon atoms,at least one of which is a member of an aromatic ring. In one form thearomatic tertiary amine can be an arylamine, such as a monoarylamine,diarylamine, triarylamine, or a polymeric arylamine. Exemplary monomerictriarylamines are illustrated by Klupfel et al. in U.S. Pat. No.3,180,730. Other suitable triarylamines substituted with one or morevinyl radicals and/or comprising at least one active hydrogen-containinggroup are disclosed by Brantley et al. in U.S. Pat. Nos. 3,567,450 and3,658,520.

A more preferred class of aromatic tertiary amines are those whichinclude at least two aromatic tertiary amine moieties as described inU.S. Pat. Nos. 4,720,432 and 5,061,569. Such compounds include thoserepresented by structural Formula A

wherein:

-   -   Q₁ and Q₂ are independently selected aromatic tertiary amine        moieties; and    -   G is a linking group such as an arylene, cycloalkylene, or        alkylene group of a carbon to carbon bond.

In one embodiment, at least one of Q1 or Q2 contains a polycyclic fusedring structure, e.g., a naphthalene. When G is an aryl group, it isconveniently a phenylene, biphenylene, or naphthalene moiety.

A useful class of triarylamines satisfying structural Formula A andcontaining two triarylamine moieties is represented by structuralFormula B

where:

-   -   R₁ and R₂ each independently represent a hydrogen atom, an aryl        group, or an alkyl group or R₁ and R₂ together represent the        atoms completing a cycloalkyl group; and    -   R₃ and R₄ each independently represent an aryl group, which is        in turn substituted with a diaryl substituted amino group, as        indicated by structural Formula C

wherein R₅ and R₆ are independently selected aryl groups. In oneembodiment, at least one of R₅ or R₆ contains a polycyclic fused ringstructure, e.g., a naphthalene.

Another class of aromatic tertiary amines are the tetraaryldiamines.Desirable tetraaryldiamines include two diarylamino groups, such asindicated by Formula C, linked through an arylene group. Usefultetraaryldiamines include those represented by Formula D

wherein:

-   -   each Are is an independently selected arylene group, such as a        phenylene or anthracene moiety;    -   n is an integer of from 1 to 4; and    -   Ar, R₇, R₈, and R₉ are independently selected aryl groups.

In a typical embodiment, at least one of Ar, R₇, R₈, and R₉ is apolycyclic fused ring structure, e.g., a naphthalene.

The various alkyl, alkylene, aryl, and arylene moieties of the foregoingstructural Formulae A, B, C, D, can each in turn be substituted. Typicalsubstituents include alkyl groups, alkoxy groups, aryl groups, aryloxygroups, and halogens such as fluoride, chloride, and bromide. Thevarious alkyl and alkylene moieties typically contain from 1 to about 6carbon atoms. The cycloalkyl moieties can contain from 3 to about 10carbon atoms, but typically contain five, six, or seven carbonatoms—e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures.The aryl and arylene moieties are usually phenyl and phenylene moieties.

The hole-transporting layer in an OLED device can be formed of a singleor a mixture of aromatic tertiary amine compounds. Specifically, one canemploy a triarylamine, such as a triarylamine satisfying the Formula B,in combination with a tetraaryldiamine, such as indicated by Formula D.When a triarylamine is employed in combination with a tetraaryldiamine,the latter is positioned as a layer interposed between the triarylamineand the electron-injecting and transporting layer. The device and methoddescribed herein can be used to deposit single- or multi-componentlayers, and can be used to sequentially deposit multiple layers.

Another class of useful hole-transporting materials includes polycyclicaromatic compounds as described in EP 1 009 041. In addition, polymerichole-transporting materials can be used such as poly(N-vinylcarbazole)(PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such aspoly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) also calledPEDOT/PSS.

Light-emitting layer 150 produces light in response to hole-electronrecombination. Light-emitting layer 150 is commonly disposed overhole-transporting layer 140. Desired organic light-emitting materialscan be deposited by any suitable way such as evaporation, sputtering,chemical vapor deposition, electrochemical means, or radiation thermaltransfer from a donor material, and can be deposited by the device andmethod described herein. Useful organic light-emitting materials arewell known. As more fully described in U.S. Pat. Nos. 4,769,292 and5,935,721, the light-emitting layers of the organic EL element comprisea luminescent or fluorescent material where electroluminescence isproduced as a result of electron-hole pair recombination in this region.The light-emitting layers can be comprised of a single material, butmore commonly include a host material doped with a guest compound ordopant where light emission comes primarily from the dopant. The dopantis selected to produce color light having a particular spectrum. Thehost materials in the light-emitting layers can be anelectron-transporting material, as defined below, a hole-transportingmaterial, as defined above, or another material that supportshole-electron recombination. The dopant is usually chosen from highlyfluorescent dyes, but phosphorescent compounds, e.g., transition metalcomplexes as described in WO 98/55561, WO 00/18851, WO 00/57676, and WO00/70655 are also useful. Dopants are typically coated as 0.01 to 10% byweight into the host material. The device and method described hereincan be used to coat multi-component guest/host layers without the needfor multiple vaporization sources.

Host and emitting molecules known to be of use include, but are notlimited to, those disclosed in U.S. Pat. Nos. 4,768,292; 5,141,671;5,150,006; 5,151,629; 5,294,870; 5,405,709; 5,484,922; 5,593,788;5,645,948; 5,683,823; 5,755,999; 5,928,802; 5,935,720; 5,935,721; and6,020,078.

Metal complexes of 8-hydroxyquinoline and similar derivatives (FormulaE) constitute one class of useful host materials capable of supportingelectroluminescence, and are particularly suitable for light emission ofwavelengths longer than 500 nm, e.g., green, yellow, orange, and red.

wherein:

-   -   M represents a metal;    -   n is an integer of from 1 to 3; and    -   Z independently in each occurrence represents the atoms        completing a nucleus having at least two fused aromatic rings.

From the foregoing it is apparent that the metal can be a monovalent,divalent, or trivalent metal. The metal can, for example, be an alkalimetal, such as lithium, sodium, or potassium; an alkaline earth metal,such as magnesium or calcium; or an earth metal, such as boron oraluminum. Generally any monovalent, divalent, or trivalent metal knownto be a useful chelating metal can be employed.

Z completes a heterocyclic nucleus containing at least two fusedaromatic rings, at least one of which is an azole or azine ring.Additional rings, including both aliphatic and aromatic rings, can befused with the two required rings, if required. To avoid addingmolecular bulk without improving on function the number of ring atoms isusually maintained at 18 or less.

The host material in light-emitting layer 150 can be an anthracenederivative having hydrocarbon or substituted hydrocarbon substituents atthe 9 and 10 positions. For example, derivatives of9,10-di-(2-naphthyl)anthracene constitute one class of useful hostmaterials capable of supporting electroluminescence, and areparticularly suitable for light emission of wavelengths longer than 400nm, e.g., blue, green, yellow, orange or red.

Benzazole derivatives constitute another class of useful host materialscapable of supporting electroluminescence, and are particularly suitablefor light emission of wavelengths longer than 400 nm, e.g., blue, green,yellow, orange or red. An example of a useful benzazole is2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole].

Desirable fluorescent dopants include perylene or derivatives ofperylene, derivatives of anthracene, tetracene, xanthene, rubrene,coumarin, rhodamine, quinacridone, dicyanomethylenepyran compounds,thiopyran compounds, polymethine compounds, pyrilium and thiapyriliumcompounds, derivatives of distryrylbenzene or distyrylbiphenyl,bis(azinyl)methane boron complex compounds, and carbostyryl compounds.

Other organic emissive materials can be polymeric substances, e.g.polyphenylenevinylene derivatives, dialkoxy-polyphenylenevinylenes,poly-para-phenylene derivatives, and polyfluorene derivatives, as taughtby Wolk et al. in commonly assigned U.S. Pat. No. 6,194,119 B1 andreferences cited therein.

While not always necessary, it is often useful that OLED device 110includes an electron-transporting layer 155 disposed over light-emittinglayer 150. Desired electron-transporting materials can be deposited byany suitable way such as evaporation, sputtering, chemical vapordeposition, electrochemical means, thermal transfer, or laser thermaltransfer from a donor material, and can be deposited by the device andmethod described herein. Preferred electron-transporting materials foruse in electron-transporting layer 155 are metal chelated oxinoidcompounds, including chelates of oxine itself (also commonly referred toas 8-quinolinol or 8-hydroxyquinoline). Such compounds help to injectand transport electrons and exhibit both high levels of performance andare readily fabricated in the form of thin films. Exemplary ofcontemplated oxinoid compounds are those satisfying structural FormulaE, previously described.

Other electron-transporting materials include various butadienederivatives as disclosed in U.S. Pat. No. 4,356,429 and variousheterocyclic optical brighteners as described in U.S. Pat. No.4,539,507. Benzazoles satisfying structural Formula G are also usefulelectron-transporting materials.

Other electron-transporting materials can be polymeric substances, e.g.polyphenylenevinylene derivatives, poly-para-phenylene derivatives,polyfluorene derivatives, polythiophenes, polyacetylenes, and otherconductive polymeric organic materials such as those listed in Handbookof Conductive Molecules and Polymers, Vols. 1-4, H. S. Nalwa, ed., JohnWiley and Sons, Chichester (1997).

An electron-injecting layer 160 can also be present between the cathodeand the electron-transporting layer. Examples of electron-injectingmaterials include alkaline or alkaline earth metals, alkali halidesalts, such as LiF mentioned above, or alkaline or alkaline earth metaldoped organic layers.

Cathode 190 is formed over the electron-transporting layer 155 or overlight-emitting layer 150 if an electron-transporting layer is not used.When light emission is through the anode 130, the cathode material canbe comprised of nearly any conductive material. Desirable materials havegood film-forming properties to ensure good contact with the underlyingorganic layer, promote electron injection at low voltage, and have goodstability. Useful cathode materials often contain a low work functionmetal (<3.0 eV) or metal alloy. One preferred cathode material iscomprised of a Mg:Ag alloy wherein the percentage of silver is in therange of 1 to 20%, as described in U.S. Pat. No. 4,885,221. Anothersuitable class of cathode materials includes bilayers comprised of athin layer of a low work function metal or metal salt capped with athicker layer of conductive metal. One such cathode is comprised of athin layer of LiF followed by a thicker layer of A1 as described in U.S.Pat. No. 5,677,572. Other useful cathode materials include, but are notlimited to, those disclosed in U.S. Pat. Nos. 5,059,861; 5,059,862; and6,140,763.

When light emission is viewed through cathode 190, it must betransparent or nearly transparent. For such applications, metals must bethin or one must use transparent conductive oxides, or include thesematerials. Optically transparent cathodes have been described in moredetail in U.S. Pat. No. 5,776,623. Cathode materials can be deposited byevaporation, sputtering, or chemical vapor deposition. When needed,patterning can be achieved through many well known methods including,but not limited to, through-mask deposition, integral shadow masking asdescribed in U.S. Pat. No. 5,276,380 and EP 0 732 868, laser ablation,and selective chemical vapor deposition.

Cathode materials can be deposited by evaporation, sputtering, orchemical vapor deposition. When needed, patterning can be achievedthrough many well known methods including, but not limited to,through-mask deposition, integral shadow masking as described in U.S.Pat. No. 5,276,380 and EP 0 732 868, laser ablation, and selectivechemical vapor deposition.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   5 vaporization apparatus-   10 organic material-   15 chamber-   20 base block-   25 first heating region-   30 control passage-   35 second heating region-   40 permeable member-   45 vaporization apparatus-   50 piston-   55 vaporization apparatus-   60 manifold-   65 liquid-   70 shield-   75 load lock-   80 deposition chamber-   85 OLED substrate-   90 aperture-   95 translational apparatus-   100 vacuum source-   105 rotating drum-   110 OLED device-   120 substrate-   130 anode-   135 hole-injecting layer-   140 hole-transporting layer-   150 light-emitting layer-   155 electron-transporting layer-   160 electron-injecting layer-   170 organic layers-   190 cathode

1. A method for vaporizing solid organic materials onto a substratesurface to form a film, comprising: a) providing a quantity of solidorganic material into a vaporization apparatus; b) actively maintainingby cooling the solid organic material in a first region in thevaporization apparatus to be below the vaporization temperature; c)heating a second region of the vaporization apparatus above thevaporization temperature of the solid organic material so that there isa steep thermal gradient on the order of 200° C./mm across the thicknessof the organic material between the first and second regions thatprotects all but the immediately vaporizing material from thetemperature in the second region; and d) metering, at a controlled rate,solid organic material from the first region into the second heatingregion so that a thin cross section of the solid organic material isheated at a desired rate-dependent vaporization temperature, whereby thethin cross section of solid organic material vaporizes and forms a filmon the substrate surface.
 2. The method according to claim 1 where thevaporized organic material passes through a permeable member locatedbetween the first and second regions.
 3. The method according to claim 1further including providing a deposition chamber and interrupting thevaporization and thereby reducing contamination of the depositionchamber walls and conserving the solid organic material when a substratesurface is not being coated.
 4. The method according to claim 1 where aconstant volume is maintained in the second region so as to establishand maintain a constant plume shape.
 5. The method according to claim 1wherein the first region is maintained at a constant temperature bycooling as the solid organic material is consumed.
 6. The methodaccording to claim 1 wherein the second region is maintained at aconstant heater temperature as the solid organic material is consumed.7. The method according to claim 1 further including providing a coolingbase block surrounding the solid organic material in the first regionand providing a liquid between the cooling base block and the solidorganic material in the first region to provide thermal contact and avapor-tight seal between the solid organic material and the cooling baseblock.
 8. The method according to claim 1 wherein the solid organicmaterial is metered on the surface of a rotatable drum into a secondregion at a controlled rate that varies linearly with vaporization rate.9. A method for vaporizing solid organic materials onto a substratesurface to form a film, comprising: a) providing a quantity of solidorganic material having at least two organic components into avaporization apparatus; b) actively maintaining by cooling the solidorganic material in a first region in the vaporization apparatus to bebelow the vaporization temperature of each of the organic components; c)heating a second region of the vaporization apparatus above thevaporization temperature of the solid material so that there is a steepthermal gradient on the order of 200° C./mm across the thickness of theorganic material between the first and second regions of thevaporization apparatus that protects all but the immediately vaporizingmaterial from the temperature in the second region; and d) metering, ata controlled rate, solid organic material from the first region into thesecond region so that a thin cross section of the solid organic materialis heated at a desired rate-dependent vaporization temperature of eachof the organic components, whereby each of the solid organic materialcomponents simultaneously vaporizes and forms a film on the substratesurface.
 10. The method according to claim 9 where the vaporized organicmaterial passes through a permeable member.
 11. The method according toclaim 9 further including providing a deposition chamber andinterrupting the vaporization rate and thereby minimizing contaminationof the deposition chamber walls and conserving the solid organicmaterials when a substrate surface is not being coated.
 12. The methodaccording to claim 9 where a constant volume is maintained in the secondregion so as to establish and maintain a constant plume shape.
 13. Themethod according to claim 9 wherein the first region is maintained at aconstant temperature by cooling as the solid organic material isconsumed.
 14. The method according to claim 9 further includingproviding a cooling base block surrounding the solid organic material inthe first region and providing a liquid between the cooling base blockand the solid organic material in the first region to provide thermalcontact and a vapor-tight seal between the solid organic material andthe cooling base block.